This invention relates to pipe couplers, and particularly to flexible conduits and their use in coupling together pipelines which are capable of rotating with respect to each other. This invention is of particular interest in equipment for offshore oil or natural gas extraction involving floating marine terminals which are rotated as wave directions change for purposes of maintaining stability.
A swivel-less coupling apparatus is disclosed in copending, commonly owned U.S. patent application Ser. No. 705,778, filed Feb. 26, 1985, now U.S. Pat. No. 4,597,595 to serve as a rotating link between a tubular riser column carrying oil or natural gas from a well on the ocean floor to a floating marine terminal. The apparatus is a replacement for swiveling links and flexible connectors previously used, eliminating sealing problems and mechanical stresses characteristic of swiveling links, and the limited range of rotation and other mechanical and geometrical problems characteristic of flexible connectors.
According to the disclosure of Ser. No. 705,778, the top of the riser column and the entry port of the pipeline on the floating vessel (facing downward) are secured in disc or ring-shaped elements in parallel horizontal planes which are spaced apart vertically, the upper plane (containing the vessel pipeline) fixed to the vessel and rotatable relative to the lower plane, following the rotation of the vessel. A flexible conduit connects the top of the riser column to the vessel entry port, the conduit being of sufficient length to rest on either of the two discs or rings, forming a wide circle around the axis of rotation. As one disc or ring rotates with respect to the other, the connecting conduit progressively uncoils from one and transfers to the other, forming an identical circle. Two complete revolutions are required for full transfer of the conduit from one plane to the other. Proper alignment during the transfer is maintained by a gear wheel over whose rim the conduit passes as it crosses over from one plane to the other. The gear wheel is positioned with its axis along the radius of the circle and the gear wheel itself travels around the periphery of the circle during rotation, mating with toothed tracks in the discs or rings.
The gear wheel has several disadvantages. First, it requires extra clearance beyond the circumference of the rotating element and it is typically located on the turret deck of a production vessel where space is at a premium. Second, it does not maintain tension on the crossover arc of the conduit when the arc expands due to hot fluids or high internal pressure. Third, the gear teeth require precise alignment and spacing for proper functioning of the wheel and the rotation of the elements.